1. Field of the Invention
The invention relates generally to the field of disk drives. More particularly, the invention relates to a damper for use in data storage applications.
2. Description of Related Art
A key component of any computer system is a device to store data. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are a disc that is rotated, an actuator that moves a transducer to various locations on the disc, and electrical circuitry that is used to write and read data to and from the disc. Coupled to the actuator is a head-gimbal assembly (HGA) that includes a head and metal suspension. The HGA's can be stacked together into a head-stack assembly (HSA), which is propelled across the disk surface by the actuator. The HSA may include a voice coil and a set of magnets. When electric current is passed through the voice coil, an electromagnetic field causes the voice coil to move, and in turn, the HSA moves across the disk surface. There are a variety of disc drives in use today, such as hard disc drives, zip drives, floppy disc drives. All utilize either rotary or linear actuators.
Magnetic heads read and write data on the surfaces of rotating disks that are co-axially mounted on a spindle motor. The magnetically-written “bits” of information are laid out in concentric circular “tracks” on the surfaces of the disks. The disks must rotate quickly so that the computer user does not have to wait long for a desired bit of information on the disk surface to become positioned under the head. In modern disk drives, data bits and tracks must be extremely narrow and closely spaced to achieve the high density of information per unit area of the disk surface that is desired.
The required small size and close spacing of information bits on the disk surface have consequences on the design of the disk drive device and its mechanical components. Because there is relative motion between the disk surface and the magnetic head due to the disk rotation and head actuation, any contact between the head and disk, due to mechanical shocks or vibration, can lead to tribological failure of the interface. Such tribological failure, known colloquially as a “head crash,” can damage the disk and head, and usually cause data loss. Vibration is particularly a serious problem when it occurs at or near the resonant frequencies of the disk drive components.
To reduce vibration problems in the disk drive assembly, several methods have been employed. One such method includes providing a damper on the actuator arm, head-gimbal assembly or head-stack assembly. Another method includes providing a damper disposed between adjacent load beams, as disclosed in U.S. Pat. No. 6,498,704. A further method includes interposing a damper between the outer surfaces of the hard disk drive assembly and the inner surface of a housing that contains the hard disk drive assembly, as disclosed in U.S. patent application Ser. No. 11/269,545.
Referring to FIG. 1, a typical prior art damper 9 may include a constraint material 11 and a viscoelastic layer 13. The viscoelastic material 13 may be made of a viscoelastic polymer with a double sided pressure sensitive adhesive, while the constraint material 11 may be made of aluminum, steel, zinc, copper or ceramic. The viscoelastic layer 13 absorbs and reduces external shocks or vibrations, while the constraint material 11 provides sheer damping capabilities. The viscoelastic layer 13 may be disposed between a component of the hard disk drive and the constraint material 11. Typically, a viscoelastic adhesive is used to couple the viscoelastic layer 13 to the constraint material 11. This viscoelastic adhesive may squeeze-out or otherwise migrate during damping applications. Exposure of the viscoelastic adhesive to the hard disk drive assembly also tends to attract contamination, thereby creating a contaminated hard disk drive environment.
One method for reducing the exposure of the viscoelastic adhesive is to limit exposing the adhesive, by only exposing it at the edges 15. As shown in FIG. 2, the viscoelastic adhesive is only exposed at the edge 15 where the viscoelastic layer 13 has the same width as the constraint material 11. Another method for reducing exposure of the viscoelastic adhesive is by directing the cut edge of the constraint material 11 so that the burr height 19 will cover some fraction of the exposed edge of the viscoelastic layer 13.
FIG. 3 shows an edge 17 of the viscoelastic layer 13 protected by a burr 19 of the constraint material 11. FIG. 4 shows a viscoelastic layer 13 that is not as wide as the constraint material 11. The viscoelastic layer 13 is thereby set back and burr protected.
Since the cut edge burr 19 varies in height and the nominal height only covers a fraction of the exposed edge, the edge of the viscoelastic layer 13 still remains exposed and accessible to be mechanically dislodged and to be contaminated. With an increasing demand for improved dampers for use in data storage devices, there remains a need in the art for a damper that protects the viscoelastic layer from contamination.